JPH02132395A - Multidirectional laser doppler speed indicator - Google Patents

Abstract

PURPOSE:To enable measurement even in an unmeasurable state resulting from crosstalk by dividing laser light from a single light source into >=2 beams and shifting the light frequencies of the respective beams by a constant quantity. CONSTITUTION:The irradiation light of a probe 1 which has an angular frequency omegatheta+omegaL is Dopper-shifted by passing through paths 1, 5 and 1 to generate signal light with an angular frequency omegatheta+omegaL+DELTAomegaX-DELTAomegaV. At the same time, crosstalk light which has an angular frequency omegatheta-deltaomegaV after being passed through the paths 2, 5, and 1 is made incident. A beam of angular frequency omegathetaseparated by a half-mirror 11 is mixed as reference light by a half mirror 10 and made incident. At this time, the light intensity of the reference light is set much larger than the signal light. Consequently, a crosstalk component of frequency omegaL+DELTAomegaX-DELTAomegaY after passed through the paths 1, 5, and 1 and a crosstalk component DELTAomegaY appear as the detected radio wave of a photodetector 14. Then, the crosstalk component is removed through a band-pass filter centering on DELTAomegaL because omegaL>>DELTAomegaXomegaL>>DELTAomegaY.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to laser Doppler velocity, which measures the velocity or displacement of a measured object by irradiating the measured object with a laser beam and based on the change in the optical frequency, that is, the Doppler shift. Regarding the total, in particular, 2
The present invention relates to a measuring device that simultaneously measures dimensional or three-dimensional velocity vectors with one measuring device.

[Prior art and its problems] Conventionally, when measuring a two-dimensional or three-dimensional velocity hector, two or three one-dimensional velocity meters are combined, the output from each measuring device is calculated, and a velocity vector is obtained. was looking for. In this case, the size and cost of the apparatus increase in proportion to the number of dimensions, and it is also necessary to set the measurement probe with high precision for each measurement. For example, as seen in Japanese Patent Laid-Open No. 57-93258, there is a patent for a multi-thorn one-dimensional pallor meter that uses an optical fiber and a plurality of one-dimensional velocimeters. However, the following practical problems occur in multi-dimensional measurements.

In order to increase the resolution of the measurement site, the probe light of each speedometer must be irradiated to one point. Since the object to be measured is often a surface that scatters light, scattered light from one measurement probe is collected by other probes and becomes stray light, resulting in crosstalk between the probes. The cross-link cannot be separated from the original signal, and in fact, two-speed measurement becomes impossible. This phenomenon will be explained using FIG.

FIG. 1 is an example of measuring two-dimensional velocity. In the figure, the scattering particle 5, which is the object to be measured, has a velocity vector V
, which is the velocity vector in the X direction →
→ It is decomposed into 8 and the Y-direction velocity vector vv. and,
Two-axis measurement probe 1 forming an angle between vector V and soil α
, 2, when irradiating light with angular frequencies ω1 and ω2, let the absolute value of the wave number vector of the laser beam be K, and the absolute value of the velocity l ) U, 80, becomes as in equations (1) and (2).

ΔωX = 2-K-Vx-sinc+
(1)△(J,: 24L1V1cosα
(2) The Doppler shift 1・Δω151 of the signal light passing through the path 1→5→1 and the Totsuburashi shift 1・Δω25+ of the cross 1・−k light passing through the g path 2→5→】 are (3
), as shown in equation (4).

Δω151=Δ(J x - △ω, (3)△
ω251 − (ω2−ωI)−Δω, (
4) When two independent laser beams are used as a biaxial light source, the difference ω2−ω1 in the optical frequency of the two laser beams is added to the quastoke component. Usually, the difference ω2-ω1 between the optical frequencies of two independent lasers changes randomly and greatly over time, so the angular frequency Δω251 of the crosstalk component changes irregularly. Even if it is possible to obtain ω2201, there will be two 1-tubular shift components △ depending on the direction of the speed hexle.
The magnitude relationship between ω151, Δω2, . changes, and only the original signal component Δω151 cannot be separated. For this reason, He
It is practically impossible to perform multidimensional measurements by combining a plurality of one-dimensional laser velocimeters that use a laser light source such as a -Ne laser that can only select a single frequency.

To avoid this phenomenon, there is a method of using two types of lasers with clearly different frequencies, but A. Unable to eliminate growing defects.

The present invention solves the drawback that a conventional multidimensional speedometer that combines multiple one-dimensional speedometers cannot measure when there is crosstalk light, and provides a compact laser Doppler speedometer that uses a single light source that can measure multidimensional speeds. The purpose is to provide a

[Means for solving the problem] The laser beam from a single light source is divided into two or more beams, and the optical frequency of each beam is shifted by a certain amount.
The optical frequencies of these multiple beams are set to be different from each other, the beam is used as a probe beam, the beam with an optical frequency different from each probe beam is used as a reference beam, and the detection current is passed through a bandpass filter. I got the signal I needed.

[Operation] A single light source is used, multiple beams with different optical frequencies of the probe light are used at regular intervals, and each beam is used as a reference light. In addition to dimensional velocity measurement, frequency separation eliminates crosstalk between probes.

[Example code] An embodiment of the present invention will be described using FIG. 2.

FIG. 2 is an example of a two-dimensional speedometer. In Fig. 2, 6 is a laser light source, 7 is a frequency shifter using an ultrasonic deflector,
8 is the driver of shifter 7, 9, 1 0, 11, 12
is a half mirror, 13 is a lens, 14 and 15 are PIN
It is a photodetector such as a photodiode or APD. The laser light source oscillates at an angular frequency of ω0, and the ultrasonic deflector 7 separates it into two diffracted beams: O-order and 1st-order. The first-order diffracted light has the driving angular frequency ω of the driver 8 (the frequency is shifted to ωθ + ωL, and ωL》Δω,
ωL》△ω, is set.

First, the path of the light beam incident on the photodetector 14 will be explained.

The irradiation light of probe 1 with L of angular frequency ωθ+ is 1→
Through the path 5 → 1, it undergoes a top-ra shift and ω0
The signal light has a negative angular frequency of +ωL+Δω8−Δω. At the same time, a cross 1.-k light having an angular frequency of ω0-Δω, which has passed through a path of 2→5→1, is misleading. On the other hand, as a reference light, beams of angular frequency ω0 separated by a half mirror 11 are mixed and incident on the half mirror 10. At this time,
The light intensity of the reference light is set to be sufficiently higher than that of the signal light.

As a result, what appears as the detection current of the photodetector 14 is ωL + Δω 180, which has passed through the path of 1→5→1, and the crosstalk component Δω. And ωL》 △
ω. , ωL》△ω, so if the signal is passed through a band pass filter centered on △ωL, the crosstalk component is removed.

Note that although the angular frequency of the difference between Δω151 and Δω251 is also detected by the photodetector, each signal intensity is sufficiently smaller than that of the reference light, so it is suppressed. Similarly, in the photodetector 15, the signal component △ω1+△ω8+ due to the path 2→5→2
Δω, and a crosstalk component Δω appear, and the crosstalk component Δω is removed by the bandpass filter.

FIG. 3 shows a signal processing system for determining the velocity vector.

The detection current obtained from the two photodetectors 14 and 15 is
The signal passes through bandpass filters 16 and 17 centered at ωL to remove crosstalk components, and then passes through frequency discriminators 18 and 19 that convert frequency shifts into voltages. Since the outputs of 18 and 19 are proportional to Vx Vv +V- + VV, respectively, by calculating the sum and difference of the output signals of 18 and 19 using 20 and 21, the velocity components Vx, Vy in both the X+y directions can be calculated.
is obtained as the voltage υ8, υ, including its direction.

FIG. 4 is an example of three-dimensional measurement.

Basically, it has a configuration in which two sets of the aforementioned two-dimensional speedometers are combined in orthogonal directions, but the point is that a total of three ultrasonic deflectors 22, 23, and 24 with two types of tribe frequencies are used. different.

The ultrasonic deflectors 23 and 24 are driven at an angular frequency 2ω which is twice that of the ultrasonic deflector 22. Optical frequencies ω1, ω of the four beams
2, ω3, and ω4 have a difference of ωL. These beams are irradiated from the direction along the hypotenuse of a square pyramid as shown in Figure 5, and the scattered light on the vertex 5 is captured as reflected light from the same side, and this is used as signal light and reference light. Light rays from beams with different 2ω angular frequencies are separated by a half mirror and used.

FIG. 6 shows the signal light of each beam, the crosstalk light component, the reference light component, and the angular frequency component of the detection current.

In this figure, the black spectral components are from signal light, and the diagonally shaded spectral components are from crosstalk light. Crosstalk components can be removed by passing each detection current through a bandpass filter centered on 2ωL. The detected signals from the probes ■ and ■ include velocity components in the X and y directions, and the detected signals from the probes ■ and ■ include velocity components in the y and two directions. Then, a three-dimensional velocity vector (Vx, Vv, V2) is determined by passing it through a frequency discriminator and calculating in a manner similar to that used in two-dimensional velocity measurement.

For the tip of the probe to be compact and easy to operate, an optical fiber can be used to guide the laser beam as shown in FIG. 7.

[Effects of the Invention] As described above, according to the present invention, even in a state where measurement is impossible due to crosstalk, which is a drawback of a conventional multidimensional speedometer using a plurality of one-dimensional speedometers, measurement is possible, and it is possible to perform measurements using a light source. Since a certain laser requires only one laser beam and the number of ultrasonic deflectors is small, an inexpensive and compact multidimensional velocity meter can be provided.

Furthermore, since this speedometer is of a reference light type, signal light can be obtained even in areas other than the area where the probe light intersects. Therefore, it also has the advantage of having a wider dynamic range than conventional two-beam differential velocimeters, which can only measure the area where the beams intersect. This feature is very effective for three-dimensional vibration measurement of solid objects.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining signal light and crosstalk light during two-dimensional measurement with a conventional device, Fig. 2 is a diagram showing an example of the optical system of a two-dimensional speedometer according to the present invention, and Fig. 4 is a diagram showing an example of the optical system of the three-dimensional speedometer according to the present invention, FIG. 5 is a diagram showing an example of the arrangement of the probe section of the present invention, and FIG. FIG. 7, a diagram showing the angular frequency spectrum at each point, is a diagram of an example in which an optical fiber is used at the tip of the probe. In the figure, reference numerals 1, 2, 3, and 4 indicate measurement probes 5 (light scattering particles on the object to be measured), 6 indicate laser light sources 7, and frequency shifters 8 using ultrasonic deflectors; 11, 12 are half mirrors 13, lenses 14, 15, 25, 26, 27, 28 are photodetectors 16,
17 is a bandpass filter 18; 19 is a frequency discriminator 20; 21 is an adder; 22 is a frequency shifter 23 using an ultrasonic deflector; Patent applicant Nippon Sheet Glass Co., Ltd. ti)t tt)2 a)3 W4 See! ward hypertrophy R kl-t tJJ3 ω4 W2 4kshi 2k1 key turn Kajishi Suk Llf/θ W Muza)mu ρ Za)t- 3alt 2tt)L

Claims (2)

[Claims] (1) In an optical laser Doppler velocimeter that irradiates a measured object with two or more probe lights at a fixed angle and multidimensionally measures the velocity or displacement vector of the measured object from the Doppler shift of the reflected light, 2 laser beams from a single light source
The optical frequency of each beam is divided into multiple beams, and the optical frequency of each beam is shifted by a certain amount, and the optical frequencies of the multiple beams are all set to be different, and the beam is used as a probe light. A reference light type multidimensional laser Doppler velocimeter that uses a beam with a frequency as a reference light and passes the detection current through a bandpass filter to obtain the necessary signal. (2) In a laser Doppler velocimeter with four probe lights that measure a three-dimensional velocity vector, the optical angular frequency of the four probe lights is shifted by ω_L, and the optical frequency of each probe light is used as the reference light optical frequency. 2ω_L from the angular frequency
The multidimensional laser Doppler velocimeter according to claim 1, characterized in that the beams are shifted by a certain amount.